View source for Action2/Only Callback Failure

== Introduction ==
The features
* Sound Effects
* Signals
have no regular Action2 to assign graphics. However, Action2 is still needed to make [[Callback Failed | callbacks fail]].

== Syntax ==
 <Sprite-number> * <Length> 01 <feature> 01 00
 <Sprite-number> * <Length> 02 <feature> <set-id> 01 00 00 00
This syntax consists of both an [[Action1]] and the actual [[Action2]]. See the detailed description below.

{|
!Element!![[GRFActionsDetailed|Size]]!!Description
|-
|<Sprite-number>||dec||A sequential sprite number
|-
|<length>||dec||The total number of bytes used in this action
|-
|<set-id>||B||What set-ID this action2 defines
|}

== Description ==

The syntax to use is the syntax of the regular [[Action2]] referencing Action1 spritesets. However:
* Every Action2 must reference at least one spriteset, so we must also define one via [[Action1]].
* Every Action1 must define at least one spriteset, but spritesets may contain zero sprites.

Above syntax specifies two pseudo sprites. First an [[Action1]] defining 1 spriteset with 0 sprites, then the [[Action2]] referencing only that single spriteset.

=== Sprite-number ===

This is just the number you are at.

=== Length ===

Count the number of bytes in this action.

=== set-id ===

This defines the ID of the current action 2. This ID will later be referred to by [[Action3|action 3]], or a variational/random action 2.

You can reuse action 2 IDs, and there's no restriction on the order in which they are defined.